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Igneous Rocks

Igneous Rocks. Rock vs. Mineral. Rock - a naturally formed consolidated material composed of grains of one or more minerals. Mineral - a naturally occurring element or compound with a relatively constant chemical and structural composition. Three Rock Types.

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Igneous Rocks

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  1. Igneous Rocks

  2. Rock vs. Mineral • Rock- a naturally formed consolidated material composed of grains of one or more minerals. • Mineral- a naturally occurring element or compound with a relatively constant chemical and structural composition.

  3. Three Rock Types • Igneous: Rock formed from the cooling of magma • Sedimentary: Rock formed from the accumulation and lithification (cementing) of weathered material. • Metamorphic: Rocks formed by the altering existing rock by heat and/or pressure.

  4. The Rock Cycle

  5. How do igneous rocks form? Intrusive Extrusive

  6. Identification of Igneous Rocks Texture: the size of the grains that make up the rock Mineralogy: the minerals present in the rock

  7. Textures: Phaneritic (Fan-er-itic): all large grains Aphanitic (A-fan-itic): all small grains Porphyritic (Poor-for-itic): large crystals surrounded by fine-grained matrix

  8. Terms to explain to chemistry of igneous rocks: • Mafic: (May-fik) Silica deficient igneous rocks with a high content of Magnesium, Iron, and Calcium. More dark minerals than light minerals. • Felsic: (fell-sick) Silica rich igneous rock with a high percentage of potassium and sodium. Usually lots of quartz and feldspar.

  9. Mineral content of Igneous Rocks

  10. Intrusive Structures: Rock formations caused by the cooling of magma beneath the Earth’s Surface.

  11. Formed when a volcano goes extinct (loses its heat source). The magma that was inside the volcano cools and hardens into a rock much harder than that on the surface. Eventually the volcano is weathered away, exposing the rock. Shiprock, New Mexico

  12. Devil’s Tower, WY

  13. Dikes: Magma from below is pushed up into cracks in the existing rock.

  14. Dikes from Intrusion

  15. Magma Formation • molten rock created near the subduction zone. • granitic magma ~ 650o C • geothermal gradient – 3o C/100 m • melting point increases with pressure; pressure increases with depth. • mineral melting point is lowered by water under pressure.

  16. Bowen’s Reaction Series • sequence in which minerals crystallize in cooling magma.

  17. Volcanism and Extrusive Rocks • pyroclastic (pyro = “fire”; clast = “broken”) • pyroclastic flow- mixture of gas and pyroclastic debris. • caldera- • pumice- • vesicles- • cinder cone-

  18. Extrusive Rocks pyroclastic flow (click the picture below for a short video pumice with vesicles

  19. Pyroclastic Flows

  20. volcanos cinder cone caldera

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